Steam turbines, to be more precise low-pressure steam turbines, have a blade row of final stage blades in the final stage which, because of their great length and mass in comparison to blades in other stages, are subject to correspondingly great centrifugal forces and oscillations during turbine operation. In order to damp these oscillations, each final stage blade in this blade row typically has a shroud which, on the sides facing the blades adjacent in the circumferential direction, is designed such that it in each case engages in the shroud of the adjacent blades. Furthermore, the shrouds are designed and are of such a size that the centrifugal forces are limited as much as possible, and the loads are distributed as uniformly as possible. In particular, the shrouds of final stage blades have smaller overhangs than the shrouds of other stages in the turbine.
Frequently, the final stage blades additionally have a snubber at the mid-height of the blades, in order to further damp the oscillations.
Because of the wet-steam environment, erosion damage frequently occurs on final stage blades, caused by droplets impact. Various measures are known for reducing or preventing such damage, for example from EP1609951 and JP2005133543. In EP1609951, a final stage blade is disclosed with an integrated shroud which has a step in the area of the blade leading edge which is affected by erosion damage, said step extends radially inward in the direction of the blade foot, and has a curved surface along the side of the shroud. These measures eliminate the problem zone, reducing the potential for accumulation of moisture.
JP2005133543 discloses rotating blades, inter alia, also for the final stage, whose inlet edge has an erosion shield consisting of a hardened zone which extends from the blade tip in the direction of the blade foot.
EP 1911935 discloses a final stage blade of a steam turbine having an integrated shroud, in which the trailing edge of a blade is in contact with the leading edge of the adjacent blade, by means of a torsion force. The trailing edge is in each case designed to be radially stepped for this purpose.
DE20023475 discloses a final stage blade with an integrated shroud as well as ribs on the shroud, which are used to shield blade parts against water droplets.